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Show INFLUENCE OF COMBUSTION PARAMETERS OF NO EMISSIONS x Comparison with Field Results Initial validation tests were conducted on the MSF to compare NO formation in the pilot scale facility directly with emission data from full-scale spreader-stoker units. Typical NO emissions data for coal-fired full-scale boilers are shown in Figure 2 by the solid lines. Each line refers to a specific furnace from the work of Langsjoen et al. (2). While the exact furnace stoichiometry distributions are unknown in these tests, they can be approximated by the use of the general distribution conditions which apply to most current coal-fired, field-operating stokers. Generally, 80-85 percent of the furnace air is delivered as underfire air. The remaining air is divided roughly equally between lower and upper overfire air jets. Nitric oxide emissions data from the model spreader stoker unit, operated under conditions typical of full scale practice, are also shown in Figure 2 (solid points). These tests were conducted at a firing rate of 470,000 Btu/hr. Overfire air represented 18 percent of the total air supplied to the furnace. The overfire air was introduced at 20 and 48 inches above the grate; the ratio of the air introduced at 48 inches to that at 20 inches was maintained constant at 1.15. The quantitative agreement between the pilot-scale-model spreader stoker emissions and the field testing data suggest that the pilot furnace appropriately simulates the combustion conditions which are of primary importance to NO formation. Overall Excess Air Figure 3 shows data on the influence of overall excess air at a constant bed zone stoichiometry for both coal and wood firing. The experiments were performed at two separate height levels of overfire air, 20 and 48 inches. With coal, as the amount of overfire air was varied to produce different overall stoichiometries, the level of NO emissions remained essentially constant. These results indicate that exhaust NO emissions are 25-7 |
